1. Field of the Invention
This invention relates to an apparatus and method used to analyze reservoir properties and production performance of wells using production data that may contain multiple reservoir and well types.
2. Description of the Prior Art
Procedures for production systems analysis have been employed for some time in the oil and gas industry. One such procedure employed is known as nodal systems analysis, sometimes called production systems analysis or production optimization.
Nodal systems analysis is a procedure for determining that flow rate at which an oil or gas well will produce. Further, nodal systems analysis has been used for evaluating the effect of various components on well production, such as the tubing string size, flow line size, separator pressure, choke sizes, safety valves, downhole restrictions, and well completion techniques, including gravel packing and perforating wells.
Using nodal systems analysis, petroleum engineers have been able to collect wellhead data and then solve equations which result in optimizing the entire production system downhole to obtain the most efficient objective flow rate. This procedure has been performed manually, or with the aid of a calculator or computer.
Many well production systems operate inefficiently. Operators of wells using nodal systems analysis evaluate the solutions at various nodes, or locations, such as the bottom of a well, the top of a well, or at the separator, which is located above the surface of the ground.
For example, the effect of a change in separator pressure can be illustrated using nodal systems analysis by taking the solution point at the separator. Then the separator pressure can be optimized based upon possible compressor installations to elevate the gas pressure for sales, or for gas lift systems. This is one example of how nodal systems analysis currently is employed.
In some cases, decline curve analysis has been used to analyze and interpret production rate and pressure data. Results of these decline curve analyses reveal information about reservoir properties such as skin factor and formation permeability. Furthermore, in-place fluid volumes, movable oil at current conditions, and the reservoir drainage area are all factors to be considered in such an analysis.
"Rigorous" analysis uses actual field data to make predictions rather than relying solely upon theoretical models, and therefore rigorous analysis using actual field data is preferred, if such data is available. Methodologies have been developed to model decline type curves or graphs for analysis of the depletion or injection performance of a well.
There exists in the petroleum industry computerized methods of determining basic well performance, in which the program is capable of assisting an operator with forecasting the volume or amounts of oil that may be produced from a well, or to model the effects of tubing sizes or other physical flow point restrictions. These prior methods have been limited primarily to variables dealing with the hydraulics of the wellbore.
Other prior art computer modeling methods have been used in the industry which are capable of: (1) history matching existing data to develop a reservoir description and then predicting well performance, and (2) predicting well performance using specified reservoir properties.
Importantly, these latter computer modeling methods do not contain wellbore hydraulic calculations, such as the wellbore outflow correlations and pressure loss factors. Thus, these prior methods cannot consider wellhead pressures and other such commonly measured surface production data directly within the program itself.
Reservoir production analysis and predictive methods of the prior art have been limited in their capabilities and scope. They have not generally been capable of performing in one computerized operation the appropriate consideration of all relevant reservoir parameters from production data analysis in obtaining reliable estimates of well parameters.
What has been needed in the industry is a petroleum reservoir production modeling system that fully incorporates a complete (from reservoir to wellhead) production systems analysis system for the evaluation of petroleum reservoir production performance, using industry accepted techniques of analysis. There exists a need for a reliable and efficient way for petroleum operators to determine well and formation properties in one computerized methodology, efficiently, reliably and accurately.
The petroleum industry has long needed a system for analyzing and providing a rigorous analytic reservoir inflow performance model for a variety of well types and reservoir outer boundary conditions and drainage area shapes, and which uses industry accepted production analysis techniques. These techniques accepted in the industry include material balance, decline curve analysis, and non-linear minimization procedures.
There has been a need in the industry for a logical analysis system that is capable of assisting a well operator with choosing the most reliable analysis technique, among known reservoir production analysis techniques, and also is capable of indicating to the user which analysis technique provides the most reliable estimate of each parameter.
Additionally, there has been a need for a generic statistical analysis procedure for analyzing field-recorded production data to minimize or eliminate the effects of outlier (i.e. noise) points in the data.
The invention of this application addresses these industry needs, and is more fully described below.